Google Apps is now G Suite. Same service, new name. More about the name change.

Upgrade to G Suite Basic

If you're using the legacy Free edition of Google Apps, you can upgrade to G Suite Basic and try it for free, for up to 10 users. This free trial period starts from the time you upgrade. Before your trial ends, you must either set up billing to keep using G Suite Basic or downgrade to go back to using the legacy Free version of Google Apps.

After upgrading, don't let your trial expire before either setting up billing or downgrading back to the legacy Free version of Google Apps. Otherwise your account will be suspended. If you simply let your trial expire, you'll also no longer have access to the Free version.

Set up billing for continued business features. You can set up billing at any time without prematurely ending your free trial. You won't be charged until your free trial ends or you add more than 10 users. In fact, we recommend entering your billing information well before the end of your trial to avoid having your service suspended. For details on pricing and payments, see G Suite Billing basics.

Downgrade to the Free edition to go back to using Google Apps for free.

You can't downgrade once your paid subscription begins. You can downgrade to the Free edition during your free trial period. However, once you set up billing and then either add more than 10 users or let the trial expire, the option to downgrade is no longer available.